MIC5020
Micrel
5-162
October 1998
General Description
The MIC5020 low-side MOSFET driver is designed to oper-
ate at frequencies greater than 100kHz (5kHz PWM for 2% to
100% duty cycle) and is an ideal choice for high-speed
applications such as motor control, SMPS (switch mode
power supplies), and applications using IGBTs. The MIC5020
can also operate as a circuit breaker with or without automatic
retry. The MIC5020's maximum supply voltage lends itself to
control applications using up to 50V. The MIC5020 can
control MOSFETs that switch voltages greater than 50V.
A rising or falling edge on the input results in a current source
or sink pulse on the gate output. This output current pulse can
turn on or off a 2000pF MOSFET in approximately 175ns.
The MIC5020 then supplies a limited current (< 2mA), if
necessary, to maintain the output state.
An overcurrent comparator with a trip voltage of 50mV makes
the MIC5020 ideal for use with a current sensing MOSFET.
An external low value resistor may be used instead of a
sensing MOSFET for more precise overcurrent control. An
optional external capacitor connected to the C
T
pin may be
used to control the current shutdown duty cycle from 20% to
< 1%. A duty cycle from 20% to about 75% is possible with
an optional pull-up resistor from C
T
to V
DD
. An open collector
output provides a fault indication when the sense inputs are
tripped.
The MIC5020 is available in 8-pin SOIC and plastic DIP
packages.
Other members of the MIC502x series include the MIC5021
high-side driver and the MIC5022 half-bridge driver with a
cross-conduction interlock.
MIC5020
Current-Sensing Low-Side MOSFET Driver
Ordering Information
Part Number
Temperature Range
Package
MIC5020BM
40
C to +85
C
8-pin SOIC
MIC5020BN
40
C to +85
C
8-pin Plastic DIP
Low-Side Driver with Overcurrent Trip and Retry
Features
11V to 50V operation
175ns rise/fall time driving 2000pF
TTL compatible input with internal pull-down resistor
Overcurrent limit
Fault output indication
Gate to source protection
Compatible with current sensing MOSFETs
Applications
Lamp control
Heater control
Motor control
Solenoid switching
Switch-mode power supplies
Circuit breaker
Typical Application
V
DD
Input
Fault
C
T
Gate
Sense
-
Sense
+
Gnd
150kHz max.
N-Channel
Power MOSFET
V+
MIC5020
1
2
3
4
8
7
6
5
10F
Load
R
SENSE
+11V to +50V
R
SENSE =
50mV
I
TRIP
* increases time before retry
optional*
MIC5020
Micrel
October 1998
5-163
5
Pin Description
Pin Number
Pin Name
Pin Function
1
V
DD
Supply: +11V to +50V. Decouple with
10
F capacitor.
2
Input
TTL Compatible Input: Logic high turns the external MOSFET on. An internal
pull-down returns an open pin to logic low.
3
Fault
Overcurrent Fault Indicator: When the sense voltage exceeds threshold,
open collector output is open circuit for 5
s (t
G(ON)
), then pulled low for
t
G(OFF)
. t
G(OFF)
is adjustable from C
T
.
4
C
T
Retry Timing Capacitor: Controls the off time (t
G(OFF)
) of the overcurrent
retry cycle. (Duty cycle adjustment.)
Open = 20% duty cycle.
Capacitor to Ground = approx. 20% to <1% duty cycle.
Pull-Up resistor = approx. 20% to approx. 75% duty cycle.
Ground = maintained shutdown upon overcurrent condition.
5
Gnd
Circuit Ground
6
Sense +
Current Sense Comparator (+) Input: Connect to high side of sense resistor
or current sensing MOSFET sense lead. A built-in offset in conjunction with
R
SENSE
sets the load overcurrent trip point.
7
Sense
Current Sense Comparator () Input: Connect to the low side of the sense
resistor (usually power ground).
8
Gate
Gate Drive: Drives the gate of an external power MOSFET. Also limits V
GS
to 15V max. to prevent Gate to Source damage. Will sink and source
current.
Pin Configuration
1
2
3
4
8
7
6
5
V
DD
Input
Fault
C
T
Gate
Sense
-
Sense
+
Gnd
1
2
3
4
8
7
6
5
Gate
Sense
-
Sense
+
Gnd
V
DD
Input
Fault
C
T
Block Diagram
Sense
Sense +
6V Internal Regulator
C
INT
I
1
2I
1
50mV
Input
ONE-
SHOT
V
DD
Gate
Fault
C
T
6V
OFF
ON
Fault
Normal
I
2
10I
2
Q1
Transistor Count: 82
DIP Package
SOIC Package
(N)
(M)
MIC5020
Micrel
5-164
October 1998
Electrical Characteristics
T
A
= 25
C, Gnd = 0V, V
DD
= 12V, Sense +, = 0V, Fault = Open, C
T
= Open, Gate C
L
= 1500pF unless otherwise specificed
Symbol
Parameter
Condition
Min
Typ
Max
Units
D.C. Supply Current
V
DD
= 12V, Input = 0V
0.8
2
mA
V
DD
= 50V, Input = 0V
2
10
mA
V
DD
= 12V, Input = 5V
0.8
2
mA
V
DD
= 50V, Input = 5V
4
25
mA
Input Threshold
0.8
1.4
2.0
V
Input Hysteresis
0.1
V
Input Pull-Down Current
Input = 5V
10
20
40
A
Fault Output
Fault Current = 1.6mA
0.15
0.4
V
Saturation Voltage
Note 1
Fault Output Leakage
Fault = 50V
1
0.01
+1
A
Current Limit Threshold
Note 2
30
50
70
mV
Gate On Voltage
V
DD
= 12V
10
11
V
V
DD
= 50V
14
15
18
V
t
G(ON)
Gate On Time, Fixed
Sense Differential > 70mV
2
5
10
s
t
G(OFF)
Gate Off Time, Adjustable
Sense Differential > 70mV, C
T
= 0pF
10
20
50
s
t
DLH
Gate Turn-On Delay
Note 3
400
800
ns
t
R
Gate Rise Time
Note 4
700
1500
ns
t
DLH
Gate Turn-Off Delay
Note 5
900
1500
ns
t
F
Gate Fall Time
Note 6
500
1500
ns
f
max
Maximum Operating Frequency
Note 7
100
150
kHz
Note 1
Voltage remains low for time affected by C
T
.
Note 2
When using sense MOSFETs, it is recommended that R
SENSE
< 50
. Higher values may affect the sense MOSFET's current transfer ratio.
Note 3
Input switched from 0.8V (TTL low) to 2.0V (TTL high), time for Gate transition from 0V to 2V.
Note 4
Input switched from 0.8V (TTL low) to 2.0V (TTL high), time for Gate transition from 2V to 10V.
Note 5
Input switched from 2.0V (TTL high) to 0.8V (TTL low), time for Gate transition from 11V (Gate ON voltage) to 10V.
Note 6
Input switched from 2.0V (TTL high) to 0.8V (TTL low), time for Gate transition from 10V from 2V.
Note 7
Frequency where gate on voltage reduces to 10V with 50% input duty cycle.
Absolute Maximum Ratings
Supply Voltage (V
DD
) .................................................. +55V
Input Voltage ................................................ 0.5V to +15V
Sense Differential Voltage ..........................................
6.5V
Sense + or Sense to Gnd .......................... 0.5V to +50V
Fault Voltage ............................................................... +50V
Current into Fault ....................................................... 50mA
Timer Voltage (C
T
) ..................................................... +5.5V
Operating Ratings
Supply Voltage (V
DD
) .................................... +11V to +50V
Temperature Range
SOIC ...................................................... 40
C to +85
C
Plastic DIP .............................................. 40
C to +85
C
MIC5020
Micrel
October 1998
5-165
5
0.5
1.0
1.5
2.0
2.5
3.0
3.5
5 10 15 20 25 30 35 40 45 50
I
SUPPLY
(mA)
V
SUPPLY
(V)
Supply Current vs.
Supply Voltage
V
IN
= 5V
V
IN
= 0V
700
800
900
1000
1100
1200
5
10
15
20
25
30
t
OFF
(ns)
V
SUPPLY
(V)
Turn-Off Time vs.
Supply Voltage
V
GATE
= 4V
C
L
= 1500pF
V
IN
= 0 to 5V
Sq. Wave
INCLUDES PROPAGATION DELAY
0
20
40
60
80
100
0
5
10
15
20
25
I
IN
(
A)
V
IN
(V)
Input Current vs.
Input Voltage
V
SUPPLY
= 12V
200
400
600
800
1000
1200
1x10
2
1x10
3
1x10
4
1x10
5
t
ON
(ns)
C
GATE
(pF)
Turn-On Time vs.
Gate Capacitance
V
GATE
= 4V
INCLUDES PROPAGATION DELAY
0.0
5.0
10.0
15.0
20.0
25.0
0.1
1
10
100
1000 10000
Shutdown Duty Cycle (%)
C
T
(pF)
t
ON
= 5
s
V
SUPPLY
= 12V
Overcurrent Shutdown
Retry Duty Cycle
Typical Characteristics
400
500
600
700
800
900
5 10 15 20 25 30 35 40 45 50
t
ON
(nS)
V
SUPPLY
(V)
Turn-On Time vs.
Supply Voltage
V
GATE
= 4V
C
L
= 1500pF
V
IN
= 0 to 5V Sq. Wave
INCLUDES PROPAGATION DELAY
Input
0V
TTL (H)
0V
50mV
Sense +,
Differential
Gate
Fault
0V
15V (max.)
Off
On
5s
20s
Input
0V
TTL (H)
0V
50mV
Sense +,
Differential
Gate
Fault
0V
15V (max.)
Off
On
5s
Input
0V
TTL (H)
0V
50mV
Sense +,
Differential
Gate
Fault
0V
15V (max.)
Off
On
20
30
40
50
60
70
80
-60 -30
0
30
60
90 120 150
VOLTAGE (mV)
TEMPERATURE (
C)
Sense Threshold vs.
Temperature
Timing Diagram 2. Fault Condition, C
T
= Open
Timing Diagram 3. Fault Condition, C
T
= Grounded
Timing Diagram 1. Normal Operation
MIC5020
Micrel
5-166
October 1998
source side sensing is provided by access to both
SENSE
+
and
SENSE
comparator inputs.
The adjustable retry feature can be used to handle loads with
high initial currents, such as lamps, motors, or heating
elements and can be adjusted from the C
T
connection.
C
T
to ground causes maintained gate drive shutdown follow-
ing overcurrent detection.
C
T
open, or through a capacitor to ground, causes automatic
retry . The default duty cycle (C
T
open) is approximately 20%.
Refer to the electrical characteristics when selecting a ca-
pacitor for a reduced duty cycle.
C
T
through a pull-up resistor to V
DD
increases the duty cycle.
Increasing the duty cycle increases the power dissipation in
the load and MOSFET. Circuits may become unstable at a
duty cycles of about 75% or higher, depending on the
conditions.
Caution: The MIC5020 may be damaged if the
voltage on C
T
exceeds the absolute maximum rating.
An overcurrent condition is externally signaled by an open
collector (
FAULT
) output.
The MIC5020 may be used without current sensing by
connecting
SENSE
+ and
SENSE
to ground.
Current Sense Resistors
Lead length can be significant when using low value (< 1
)
resistors for current sensing. Errors caused by lead length
can be avoided by using four-terminal current sensing resis-
tors. Four-terminal resistors are available from several
manufacturers.
Applications Information
The MIC5020 MOSFET driver is intended for low-side switch-
ing applications where higher supply voltage, overcurrent
sensing, and moderate speed are required.
Supply Voltage
A feature of the MIC5020 is that its supply voltage rating of up
to 50V is higher than many other low-side drivers.
The minimum supply voltage required to fully enhance an N-
channel MOSFET is 11V.
A lower supply voltage may be used with logic level MOSFETs.
Approximately 6V is needed to provide 5V of gate enhance-
ment.
Low-Side Switch Circuit Advantages
A moderate-speed low-side driver is generally much faster
than a comparable high-side driver. The MIC5020 can
provide the gate drive switching times and low propagation
delay times that are necessary for high-frequency high-
efficiency circuit operation in PWM (pulse width modulation)
designs used for motor control, SMPS (switch mode power
supply) and heating element control. Switched loads (on/off)
can benefit from the MIC5020's fast switching times by
allowing use of MOSFETs with smaller safe operating areas.
(Larger MOSFETs are often required when using slower
drivers.)
Overcurrent Limiting
A 50mV comparator is provided for current sensing. The low
level trip point minimizes I
2
R losses when power resistors are
used for current sensing. Flexibility in choosing drain or
Functional Description
Refer to the MIC5020 block diagram.
Input
A signal greater than 1.4V (nominal) applied to the MIC5020
INPUT
causes gate enhancement on an external MOSFET
turning the external MOSFET on.
An internal pull-down resistor insures that an open
INPUT
remains low, keeping the external MOSFET turned off.
Gate Output
Rapid rise and fall times on the
GATE
output are possible
because each input state change triggers a one-shot which
activates a high-value current sink (10I
2
) for a short time. This
draws a high current through a current mirror circuit causing
the output transistors to quickly charge or discharge the
external MOSFET's gate.
A second current sink continuously draws the lower value of
current used to maintain the gate voltage for the selected
state.
An internal 15V Zener diode protects the external MOSFET
by limiting the gate output voltage when V
DD
is connected to
higher voltages.
Overcurrent Limiting
Current source I
1
charges C
INT
upon power up. An optional
external capacitor connected to C
T
is discharged through
MOSFET Q1.
A fault condition (> 50mV from
SENSE
+ to
SENSE
) causes
the overcurrent comparator to enable current sink 2I
1
which
overcomes current source I
1
to discharge C
INT
in a short time.
When C
INT
is discharged, the
INPUT
is disabled, which turns
off the
GATE
output; the
FAULT
output is enabled; and C
INT
and C
T
are ready to be charged.
When the
GATE
output turns the MOSFET off, the overcurrent
signal is removed from the sense inputs which deactivates
current sink 2I
1
. This allows C
INT
and the optional capacitor
connected to C
T
to recharge. A Schmitt trigger delays the
retry while the capacitor(s) recharge. Retry delay is in-
creased by connecting a capacitor to C
T
(optional).
The retry cycle will continue until the the fault is removed or
the input is changed to TTL low.
If C
T
is connected to ground, the circuit will not retry upon a
fault condition.
Fault Output
The
FAULT
output is an open collector transistor.
FAULT
is
active at approximately the same time the output is disabled
by a fault condition (5
s after an overcurrent condition is
sensed). The
FAULT
output is open circuit (off) during each
successive retry (5
s).
MIC5020
Micrel
October 1998
5-167
5
Lamp Driver Application
Incandescent lamps have a high inrush current (low resis-
tance) when turned on. The MIC5020 can perform a "soft
start" by pulsing the MOSFET (overcurrent condition) until
the filament is warm enough for its current to decrease
(resistance increases). The sense resistor is selected so the
voltage across the sense resistor drops below the sense
threshold (50mV) as the filament becomes warm. The
MOSFET is no longer pulsed to limit current and the lamp
turns completely on.
V
DD
Input
Fault
C
T
Gate
Sense
-
Sense
+
Gnd
TTL Input
(0V/5V)
R
SENSE
(0.041
)
N-Channel
Power MOSFET
(IRF540)
V+
MIC5020
1
2
3
4
8
7
6
5
10F
Incandescent
Lamp (#1157)
(+11V to +12V)
"( )" values apply to
demo circuit. See text.
Figure 1. Lamp Driver with
Current Sensing
A lamp may not fully turn on if the filament does not heat up
adequately. Changing the duty cycle, sense resistor, or both
to match the filament characteristics can correct the problem.
Soft start can be demonstrated using a #1157 dual-filament
automotive lamp. The value of R
S
shown in figure 1 allows for
soft start of the higher-resistance filament (measures approx.
2.1
cold or 21
hot).
Solenoid Driver Application
The MIC5020 can be directly powered by the control voltage
supply in typical 11Vdc through 50Vdc control applications.
Current sensing has been omitted as an example.
V
DD
Input
Fault
C
T
Gate
Sense
-
Sense
+
Gnd
TTL Input
N-Channel
Power MOSFET
V+
MIC5020
1
2
3
4
8
7
6
5
10F
Diode
Solenoid
+11V to +50V
Figure 2. Solenoid Driver,
Without Current Sensing
A diode across the load protects the MOSFET from the
voltage spike generated by the inductive load upon MOSFET
turn off. The peak forward current rating of the diode should
be greater than the load current.
Current Sensing MOSFET Application
A current sensing MOSFET allows current sensing without
adding additional resistance to the power switching circuit.
A current sensing MOSFET has two source connections: a
"power source" for power switching and a "current source" for
current sensing. The current from the current source is
approximately proportional to the current through the power
source, but much smaller. A current sensing ratio (I
SOURCE
/
I
SENSE
) is provided by the MOSFET manufacturer.
V
DD
Input
Fault
C
T
Gate
Sense
-
Sense
+
Gnd
TTL Input
(0V/5V)
N-Channel
Current Sensing
Power MOSFET
V+
MIC5020
1
2
3
4
8
7
6
5
10F
Load
R
SENSE
(10
)
+11V to +50V
(+13.2V)
(+13.2V, > 4.4A)
(IRCZ24)
(3
, > 60W)
"( )" values apply to
demo circuit. See text.
Figure 3. Using a Current Sensing MOSFET
The MOSFET current source is used to develop a voltage
across a sense resistor. This voltage is monitored by the
MIC5020 (
SENSE
+ and
SENSE
pins) to identify an overcur-
rent condition.
The value of the sense resistor can be estimated with:
R
SENSE
= (r V
TRIP
R
DS(ON)
) / (I
LOAD
R
DS(ON)
V
TRIP
)
where:
R
SENSE
= external "sense" resistor
V
TRIP
= 50mV (0.050V) for the MIC5020
r = manufacturer's current sense ratio: (I
SOURCE
/I
SENSE
)
R
DS(ON)
= manufacturer's power source on resistance
I
LOAD
= load current (power source current)
The drain to source voltage under different fault conditions
affects the behavior of the MOSFET current source; that is,
the current source will respond differently to a slight over-
current condition (V
DS(ON)
very small) than to a short circuit
(where V
DS(ON)
is approximately equal to the supply voltage).
Adjustment of the sense resistor value by experiment starting
from the above formula will provide the quickest selection of
R
SENSE
.
Refer to manufacture's data sheets and application notes for
detailed information on current sensing MOSFET character-
istics.
Figure 3 includes values which can be used to demonstrate
circuit operation. The IRCZ24 MOSFET has a typical sense
ratio of 780 and a R
DS(ON)
of 0.10
. A large 3
wirewound
load resistor will cause inductive spikes which should be
suppressed using a diode (using the same configuration as
figure 2).
MIC5020
Micrel
5-168
October 1998
Faster MOSFET Switching
The MIC5020's
GATE
current can be multiplied using a pair
of bipolar transistors to permit faster charging and discharg-
ing of the external MOSFET's gate.
V
DD
Input
Fault
C
T
Gate
Sense
-
Sense
+
Gnd
150kHz max.
N-Channel
Power MOSFET
(IRF540)
+40V max.
MIC5020
1
2
3
4
8
7
6
5
10F
Load
+11V to +50V
2N3904
2N3906
Figure 4. Faster MOSFET Switching Circuit
NPN and PNP transistors are used to respectively charge
and discharge the MOSFET gate. The MIC5020 gate current
is multiplied by the transistor
.
The switched circuit voltage can be increased above 40V by
selecting transistors with higher ratings.
Remote Overcurrent Limiting Reset
In circuit breaker applications where the MIC5020 maintains
an off condition after an overcurrent condition is sensed, the
C
T
pin can be used to reset the MIC5020.
V
DD
Input
Fault
C
T
Gate
Sense
-
Sense
+
Gnd
TTL input
N-Channel
Power MOSFET
V+
MIC5020
1
2
3
4
8
7
6
5
10F
Load
R
SENSE
+11V to +50V
74HC04
(example)
Q1
2N3904
10k to
100k
Retry (H)
Maintained (L)
Figure 5. Remote Control Circuit
Switching Q1 on pulls C
T
low which keeps the MIC5020
GATE
output off when an overcurrent is sensed. Switching Q1 off
causes C
T
to appear open. The MIC5020 retries in about
20
s and continues to retry until the overcurrent condition is
removed.
For test purposes, a 680
load resistor and 3
sense resistor
will produce an overcurrent condition when the load's supply
(V+) is approximately 12V or greater.
Low-Temperature Operation
As the temperature of the MIC5020AJB (extended tempera-
ture range version--no longer available) approaches 55
C,
the driver's off-state, gate-output offset from ground in-
creases. If the operating environment of the MIC5020AJB
includes low temperatures (40
C to 55
C), add an external
2.2M
resistor as shown in Figures 6a or 6b. This assures
that the driver's gate-to-source voltage is far below the
external MOSFET's gate threshold voltage, forcing the
MOSFET fully off.
V
DD
Input
Fault
C
T
Gate
Sense
Sense
Gnd
V+
MIC5020
1
2
3
4
8
7
6
5
10F
Load
R
SENSE
+11V to +50V
2.2M
Figure 6a. Gate-to-Source Pull Down
The gate-to-source configuration (refer to Figure 6a) is ap-
propriate for resistive and inductive loads. This also causes
the smallest decrease in gate output voltage.
V
DD
Input
Fault
C
T
Gate
Sense
Sense
Gnd
V+
MIC5020
1
2
3
4
8
7
6
5
10F
Load
R
SENSE
+11V to +50V
2.2M
Figure 6b. Gate-to-Ground Pull Down
The gate-to-ground configuration (refer to Figure 6b) is
appropriate for resistive, inductive, or capacitive loads. This
configuration will decrease the gate output voltage slightly
more than the circuit shown in Figure 6a.
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